PEKTACEROS SQUAMATUS. 83 



They appear to imbricate slightly at their margins. The breadth of the fourth 

 supero-marginal is 7 mm., the length 4 mm., and the height 3'5 mm. The height 

 of the ray at this point is 12' 2 mm. 



The infero -marginal plates are opposite to the supero-marginals. They are 

 approximately about the same size and number. Between the supero- and infero- 

 marginal series a triple series of intermarginalia occurs in the interradial areas. 

 The inner and larger intermarginals persist throughout the greater part of 

 the length of the arm. It is this intercalated series which gives to the arm its 

 great proportionate depth. The outer and smaller series disappear at about the 

 seventh and ninth infero-marginal plates. 



The ornamentation of the plates appears to have been worn away, although 

 upon many of the plates a distinct marginal area may be seen. 



Upon most of the plates there occur small entrenched pedicellarise which are 

 very characteristic of this species of Pentaceros. They consist of a small pit from 

 which radiate two fine entrenchments (see PI. XXIV, fig. 2 a). 



One of the rows of specimen no. B. 2562 is distorted so as to bring the ventral 

 surface into view. This shows that the ventro-lateral plates extend well towards, 

 and perhaps all the way to, the extremities of the arm. 



Locality and Stmtigraphical Position. The locality of the type specimen is 

 given as Lower Chalk, Washington, Sussex. The specimen registered E. 2562 is 

 from the Lower Chalk, Burham, Kent, and the specimen in the Museum of 

 Practical Geology is from the Lower Chalk, Dover. 



Remarks. The specimen registered E. 2562 presents only one or two pedi- 

 cellaria?, which are so characteristic and numerous on the other two specimens. 



4. PENTACEROS SQUAMATUS, Forbes, sp. PI. XXV, figs. 3, 3 a, 3 b, 3 c. 



OREASTEK SQTJAMATUS, Forbes, 1848. Mem. Geol. Surv. Gt. Brit., vol. ii, p. 468. 



Forbes, 1850. In Dixon's Geology and Fossils of the 

 Tertiary and Cretaceous Formations of Sussex, 

 p. 328, pi. xxiii, fig. 7. 

 Dujardin et HupS, 1862. Hist. Nat. Zooph. Echin. (Suites. 



k Buff on), p. 389. 



_ _ Forbes, 1878. In Dixon's Geology of Sussex (new edition, 



Jones), pp. 363, 370, pi. xxiii, fig. 7. 



Specific Characters. Disc high, with conspicuous primary radialia, inter- 



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